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Seaview Wastewater Treatment Plant

At the Seaview Treatment Plant, sewage travels through a series of screens, tanks, bioreactors, clarifiers and ultraviolet treatments before being discharged as liquid into Bluff Point, south of the Pencarrow Lighthouse.

The current consent ‘WGN120142 [33408] Discharge Treated Wastewater to Stream (Seaview WWTP)’ expired in 2018. Prior to the expiry of this consent, HCC applied to Greater Wellington Regional Council (GWRC) for a new consent to temporarily discharge treated wastewater from the Seaview WWTP to the Waiwhetu Stream. While this process is underway, we continue to operate under the existing consent.

In general, the consents allow HCC to:

  • discharge of treated and partially treated effluent through an existing outfall,
  • to discharge mixed disinfected, treated and milli-screened wastewater during and/or immediately after heavy rainfall,
  • to discharge mixed disinfected, treated and milli-screened wastewater during maintenance,
  • the discharge of contaminants to the air,
  • and permission to occupy the stream and coastal marine area with an outfall structure.


Biofilter Media Replacement - Summer 2023

From November 14, the treatment plant operator, Veolia, will be replacing the plant's biofilter media to help reduce odour levels. 

During the works, residents and businesses in the immediate area may sometimes experience stronger levels of odour than usual while the filter media is replaced.

The biofilter reduces the odour produced by the wastewater treatment process and is replaced periodically to remain effective. 

To minimise odour levels during replacement, Veolia will have odour blasters operating and will replace media in each of the six cells, one at a time, to reduce the odour as much as possible.

The total filter replacement process is expected to take three months to complete.

Investigation Reports

Seaview Wastewater Treatment Plant - Odour Investigation - June 2023

Frequently Asked Questions

How does biofiltration work at a treatment plant?

Air and gases from the most odorous wastewater treatment processes are extracted through a ventilation system and blown through an active biological bed of bark and other organic material, which make the biofilter.

As it works its way through this natural bark mix, the bacteria in the biofilter break down the odours until the air reaches the top and is released as neutralised air.

What to expect

Residents and businesses in the immediate area of the plant may experience stronger levels of odour than normal. Unfortunately, this is unavoidable, but we will have odour blasters in operation during the works to minimise odour. The total programme may take up to three months to complete, but stronger odours should only be expected for short intermittent periods while the bacteria establish in the new bark. There will also be higher than usual heavy transport movements periodically to and from the site, as the biofilter material is removed and replaced.

How often is it replaced?

It depends on the state of the media and typically replacement may be required between 5 to 10 years.

Why can it not be done without creating an odour?

The bacteria in the bark take some time to fully develop when the new bark is placed into operation, so the treatment in that cell will not be as effective in the initial period. The cells will be replaced gradually to minimise odour.

Why does it have to be done over summer when the odour could potentially feel worse in the heat?

 The replacement of the biofilter has been programmed to start before the end of this year. There is no ideal time to do this replacement. Whether the works are in summer or winter, wind may affect odour levels.

What do the odour blasters do?

The odour blasters send diluted chemical mixture into the air to neutralise and mask offensive odour from the wastewater process areas.

Why can’t you move and replace all the cells at once and get it done faster?

We expect there will be less odour if the replacement process is done in stages.

Who do we contact if the odour is affecting our health?

If you have a complaint about Wellington Water directly, please call 04 912 4470 or email to access our free complaints process.

After hours, please contact the Hutt City Council Call Centre on 04 570 6666 / 0800 488 824.

Greater Wellington Regional Council is the regulatory agency for reporting airborne discharges 0800 496 734.  

Monthly reporting summary

December 2021

There were 2 consented bypass discharges for this month, both due to wet weather,

Algae growth continues to be a problem for the plant,

Biofilters are inspected monthly to avoid odour in the neighbourhood.

November 2021

No bypass discharge for the month,

Heavy metal levels in effluent are well below consent limits,

Faecal coliforms and Enterococci levels from shoreline monitoring are well below freshwater guidelines,

Algae growth in the clarifiers affected UV performance. A temporary system was put in place to continuously remove the algae from the clarifiers.

Resource consents

Resource consent reports

Plant performance

Current Status: Non- compliant 
Period: October 2023


The plant remains non-compliant for faecal coliforms (90-day, 80th percentile limit) since 30 September. 


The plant had one consented discharge to the Waiwhetu Stream on 25 October due to high flows during a wet weather event, discharging fully treated effluent. 

Odour complaints:

The plant received two odour complaints in October.

Items of significance:

Biofilter remedial works

Physical works to remove and replace the media will commence 14 November. Testing of current media was required for landfill disposal assurance and these test results came back within the landfill parameters. The project scope includes remedial works to the pipework located below the media. The project is expected to take 2-3 months to complete however the biofilters performance is expected to improve significantly as the works progress.

Odour Treatment:

What has been completed

The planned odour survey and odour control system assessment report has been completed with several recommendations made. 

A project brief for the renewal of the odour control system of the site has also been completed, incorporating the recommended actions from the investigation reports. The project is in response to the Abatement Notice that was issued by GWRC in April. The project has been assigned to Wellington Water’s Major Projects Team to manage.

What is currently in progress:

WWL’s Major Projects Team have assigned the project via the consultant panel. Project planning is underway.